1. Technical Field
The present invention relates in general to nanoimprinting and, in particular, to an improved system, method, and apparatus for providing a non-contact, diffuse exposure for making a photopolymer nanoimprinting stamper.
2. Description of the Related Art
Nanoimprinting may be the most feasible technology for enabling the concept of patterning recording media into products. However, because of the extremely high cost to fabricate a master, direct imprinting by using the original master to mass produce disk replicas would be lifetime limited. There also would be a high risk of damaging the original master during the imprinting operation.
One method of overcoming these challenges is to use a “daughter master” in which the disk replica imprinting is separated into two stages. In the first stage, the original master is used to create numerous, inexpensive daughter stampers. Then, in the second stage, the daughter stampers are used to imprint many disk replicas.
For example, FIGS. 1-4 depict one method of fabricating daughter stampers. As shown in FIG. 1, a droplet of stamper resist 21 is positioned on an original silicon master 23, which is spaced apart from a stamper backing plate 25 having a gel pad 27. Under pressure (FIG. 2), the plate 25 contacts and distributes the resist 21 across master 23. As shown in FIG. 3, a UV cure 29 then cures the resist 21 to form a patterned stamper layer 30 (FIG. 4) or daughter master/stamper on the plate 25.
Referring now to FIGS. 5-8, one method of a disk replica imprinting process is described. As shown in FIG. 5, a droplet of replica resist 31 is positioned on a substrate 33, which is spaced apart from the daughter stamper 30 on plate 25 and gel pad 27. Under pressure (FIG. 6), the daughter stamper 30 contacts and distributes the resist 31 across substrate 33. As shown in FIG. 7, a UV cure 39 then cures the resist 31 to form a patterned replica layer 40 (FIG. 8) on the substrate 33.
Another problem that may be encountered during these fabrication processes is the formation of defects and undesirable stamper surface dimples. For example, as shown in FIGS. 9-11, the stamper backing plate 25 can accumulate defects or contaminants 41 (FIG. 9), such as debris, fibers, imperfections, etc. During the daughter stamper fabrication process (FIG. 10), the gel pad 27 and plate 25 are pressurized as shown. The contaminants 41 force bulges 43 to appear on the opposite surface of plate 25 on which they reside, in this case, the bottom of plate 25. This is due to the propagation of the elastic deformation of the plate 25. After UV curing 29, the surface bulges 43 introduce local spots that thin the daughter stamper 30 as shown. Upon releasing the pressure (FIG. 11), the bottom plate surface elastically recovers to its original shape (i.e., flat) and, as a result, the thin spots in the daughter stamper 30 form stamper dimples 45. The stamper dimples 45 cause undesirable base layer thickness non-uniformity on the imprinted replica, which then results in non-uniform pattern transfer to the disk substrates after RIE.
Yet another potential problem source occurs during the UV curing process of fabricating daughter stampers. As shown in FIG. 12, the UV radiation is emitted as a collimated beam. Any additional defects or contaminants 47, such as other types of debris or particles, form shadows 49 on the resist 21 when the collimated UV light 29 passes through the gel pad 27 and plate 25. These shadows 49 form areas 50 of uneven UV exposure intensity along the stamper layer/master interface and cause additional surface topography and, thus, surface imperfections. The unevenness in the UV light intensity is due to the shadowing effect of the contaminants 49 that reside in the path of the UV beam.
There is usually considerable volume shrinkage (about 10%) of a photopolymer after UV cure. In addition, the mechanical properties of the photopolymer also change with the polymerization process. This change is far more significant from the liquid to solid states than the volume shrinkage. Considering all of the changes of the resist properties that are progressing with the level of curing, it is expected that there is a rather complicated thermal-mechanical interaction and stress balancing acts between the shaded areas and the background photopolymer layer.
The replica thickness patch defects can have a significant negative impact on the quality of the disk replicas due to their relatively large size and high defect density. These defects can be easily detected from the background by the color contrast, which reflects their base layer thickness variations. The base layer thickness distribution among these defects ranges from about 50 to 200 nm, which is much thicker than that of the uniform area (about 20 nm or less). Consequently, these defects prevent a uniform pattern transfer during the reactive ion etch (RIE) process used to make patterned disk substrates.
It is almost impossible to completely remove the impurities embedded in the gel pad (e.g., air bubbles, impurities, etc.), surface defects (e.g., scratches) on plates, or airborne debris particles, etc., from an imprinting system. To demand perfect quality for every material in use and perfectly clean environment for the nanoimprinting operation is very costly if not impossible. Rather than perfecting everything involved in an imprinting operation, it would be more desirable to compensate for the root causes of the problems. Thus, an improved system, method, and apparatus for making photopolymer nanoimprinting stampers that avoid these issues would be desirable.